Conventionally, on the surface of a spectacle lens, in order to enhance transmittance and to obtain a clear field of vision, an antireflection film made of a multilayer film of dielectric layers is formed. Since a spectacle lens has a purpose of vision correction, it is used under various circumstances different in conditions such as, for example, temperature, humidity, the inside of a building, and the outside of a building. Therefore, characteristics of the antireflection film are also required not to change under such various use environments.
However, in recent years, the mainstream of raw material of a spectacle lens has moved from an inorganic glass to a plastic raw material that is lightweight and is not easily broken, and it is not easy to maintain adhesiveness between a plastic base material being an organic material and an antireflection film containing an inorganic dielectric substance.
Specifically, plastic base materials have a feature of low melting temperature and low thermal deformation temperature. In addition, plastic base materials have a problem of gas emission from the inside thereof. Accordingly, it is not possible to perform a heating treatment of a base material, also on a plastic base material, at a temperature of 300° C. to 400° C., which is performed in the formation of an evaporation film on a base material made of inorganic glass. If a heating treatment at a temperature of 300° C. to 400° C. is possible also for a plastic base material, the formation of an antireflection film excellent in adhesiveness and durability is possible on the plastic base material, but since there are above-mentioned feature, problems and the like, conventionally, an antireflection film is formed on a plastic base material at a low temperature of not higher than 60° C. to 80° C. Consequently, the adhesive force of the antireflection film for the plastic base material and the durability thereof are low.
Therefore, conventionally, in order to solve the above-mentioned problems of the antireflection film, various technologies are proposed (see, for example, Patent Literatures 1 to 3). In Patent Literatures 1 to 3, there are proposed technologies of forming an antireflection film with good adhesiveness directly on a plastic base material, and in Patent Literature 1, there is proposed a technique of providing a metal film, as an adhesive layer, at a first layer of an antireflection film on the base material side and forming an antireflection film made of a dielectric layer on the metal film. In addition, in Patent Literature 2, there is proposed a technique of forming a chromium oxide film as an adhesive layer, and after that, forming an antireflection film on the adhesive layer. Furthermore, in Patent Literature 3, there is proposed a technique of forming a silicon monoxide film as an adhesive layer, and after that, forming an antireflection film on the adhesive layer. Plastic lenses manufactured by techniques described in the above-mentioned Patent Literatures 1 to 3 are used mainly as an optical lens built in a camera and the like.
However, each of materials of adhesive layers used in the above-mentioned Patent Literatures 1 to 3 is a colored material having an absorption band in visible light. Therefore, the application of antireflection films proposed in the above-mentioned Patent Literatures 1 to 3 to spectacle lenses, for which visual transparency (being colorless and transparent) is required, is difficult. Therefore, conventionally, in spectacle lenses, the coating of a hard coat material containing SiO2 sol on a plastic base material forms a hard coat layer, and on the hard coat layer, an antireflection film is formed (for example, see Patent Literature 4).
In addition, conventionally, in order to enhance weather resistance and adhesiveness of an antireflection film, a technology of forming a foundation layer containing Al2O3 on a plastic substrate with a hard coat, and furthermore, forming an antireflection film on the foundation layer is also proposed (for example, see Patent Literature 5).